rash

About 3 months ago, I had protected vaginal sex with a female. After I ejaculated, she also performed unprotected oral sex on me. About 2 weeks ago I noticed a small pinkish rash on my inner thigh, next to my testicles. I have no bumps or rash on my scrotum or penis, just this small rash on my inner thigh. It doesn't even itch really, just kinda bothers every once in a while.

My question is, should I be concerned I have an STD? I've been looking into it, but so far I'm not sure if I do or not.